add missing copyright header

gitlab/exceptions.py

@@ -1,3 +1,20 @@
+# -*- coding: utf-8 -*-
+#
+# Copyright (C) 2013-2015 Gauvain Pocentek <gauvain@pocentek.net>
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Lesser General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
 class GitlabError(Exception):
     def __init__(self, error_message="", response_code=None,
                  response_body=None):